Measurement of CMRO₂ in Neonates Undergoing Intensive Care Using Near Infrared Spectroscopy

Abstract

Greater understanding of the rate of oxygen delivery and uptake in sick preterm and term infants undergoing intensive care is an important aim of brain-orientated neonatal medicine. Near infrared spectroscopy (NIRS) is a continuous, non-invasive and portable technique which can be used to measure cerebral blood flow (CBF) in infants. It is also possible to use spatially resolved spectroscopy to measure absolute mean cerebral oxygen saturation (SmcO₂). The aim of this study was to investigate the derivation of cerebral metabolic rate for oxygen (CMRO₂) from these two measurements. Nine preterm infants were studied, of median (range) gestational age 25 (23–37) weeks. A NIRO300 was used to measure CBF and SmcO₂ simultaneously over the right and left hemisphere. Median (range) left and right cerebral hemisphere values for CMRO₂ were 0.95 (0.79–1.53) ml 100g⁻¹.min⁻¹ and 0.88 (0.69–1.46) ml 100g⁻¹.min⁻¹, respectively. No significant difference was seen between the left- and right-sided values. These values are similar to median (range) values previously reported in infants using positron emission tomography or more invasive NIRS methods. Further work is necessary to define limits on the use of this technique, particularly in the assumption of the venous:arterial compartment volume ratio across different infants.